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<title>PREDOM: How it works</title>
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    <a href="SP_0_Main.htm"><img src="images/abacus.gif" border="0" width="32" height="32" alt="Calc." title="Calc."></a>&nbsp;</td>
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<h3>PREDOM: Predominance Area Diagrams</h3>

<h3>How it works</h3>

<p><b>PREDOM</b> uses a point to point technique, which is slow, and has a plot
resolution that depends on the interval between points. The advantage is that
<nobr>log(<i>Tot.Conc.</i>)</nobr> can be the variable in an axis.</p>
<ul>
<li>The concentration area to be studied is divided with 50 steps in each axis,
		giving a grid of 2601 chemical compositions to solve. Larger grids
		(smaller steps) may be selected by the user.</li>
<li>For every point in the grid, the mass-balance equations are solved
		(if the <nobr>Tot. Conc.</nobr> is given for at least one component) by calling the
		<a href="SP_Haltafall.htm">HALTAFALL</a> algorithm, and then the species
		distribution is determined.</li>
<li>If no solid is present, the predominant soluble species is the one with a
    highest fraction of the main component.
		For example, for <nobr>Fe<sub>2</sub>(OH)<sub>2</sub><sup>4+</sup>,</nobr> the
		fraction is <nobr><b>2</b>[Fe<sub>2</sub>(OH)<sub>2</sub><sup>4+</sup>]/[Fe]<sub>TOT</sub></nobr>
		while for <nobr>Fe(OH)<sub>2</sub><sup>+</sup>,</nobr> the fraction is
		<nobr>[Fe(OH)<sub>2</sub><sup>+</sup>]/[Fe]<sub>TOT</sub>.</nobr>  Therefore, the first
		complex will dominate over the second only if <nobr>[Fe<sub>2</sub>(OH)<sub>2</sub><sup>4+</sup>]</nobr>
		&gt; <nobr>&frac12;[Fe(OH)<sub>2</sub><sup>+</sup>].</nobr></li>
<li>If at least one <i>solid</i> is formed by the main component, the predominating species
	  in the diagram will be the solid with the largest fraction of the main component.
		In this case the predominant species in the plot is the solid, even in the case
		where the solid's concentration (mol/L) is smaller than the predominating aqueous
		species.</li>
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